1. Field of the Invention
The present invention relates to a pneumatic tire and a manufacturing method therefor, the pneumatic tire including: a carcass layer bridged between a pair of bead portions; and an inner liner layer disposed at a tire inner surface side of the carcass layer, the inner liner layer being made of a thermoplastic resin or a thermoplastic elastomer composition obtained by blending a thermoplastic resin with an elastomer. More particularly, the present invention relates to a pneumatic tire and a manufacturing method therefor which allow a reduction in a cavity resonance sound without complicated manufacturing steps.
2. Description of the Related Art
A cavity resonance phenomenon that occurs in a cavity portion formed between a pneumatic tire and a rim of a wheel has been a major cause of tire noises. For example, the cavity resonance phenomenon is involved in: a noise having a frequency of around a 250 Hz, which is heard consistently during running; and an impact sound which is generated when the tires run over a joint in a road, or the like.
Conventionally, as a proposed technique for reducing a noise due to such a cavity resonance phenomenon, a rubber-made partition plate extending in a tire width direction is attached to a tire inner surface. Thereby, the cavity resonance mode is changed to reduce the sound pressure level (for example, Japanese patent application Kokai publication No. Hei. 5-294102). However, when such a rubber-made partition plate is attached to the tire inner surface after curing, a mold releasing agent used during the curing may have adhered to the tire inner surface, or the uneven pattern of a curing bladder may have been transferred to the tire inner surface. Accordingly, the partition plate tends to be attached incompletely. For this reason, repeated deformation of the tire due to the rolling thereof causes the partition plate to be detached from the tire inner surface after an extended period of use. As a result, this technique has a durability problem and also has a problem that it is difficult to keep the noise-reducing effect over an extended period.
As this countermeasure, the following proposals have been made. In one of the proposals, first, a film made of a material mainly composed of a thermoplastic resin is folded. The film having the folded portions is used to form an inner liner layer. Then, the folded portions are erected inward in a tire radial direction after the tire is cured. In another proposal, a film made of a material mainly composed of a thermoplastic resin is used to form an inner liner layer. Then, thin films made of the same material as that of the inner liner layer are thermally fused with the inner liner layer to serve as partition plates (for example, Japanese patent application Kokai publication No. 2007-62541). However, the operation of erecting the folded portions and the operation of thermally fusing the thin films are complicated. These techniques have not been practically adopted yet.